Microelectro-mechanical Systems (MEMS) microphones are commonly used in low power, battery operated devices that are sensitive to power consumption, such as, smartphones and tablet computers. MEMS microphones are popular with these applications because MEMS microphones can be implemented as a pressure sensitive diaphragm that is etched directly onto a silicon die with standard lithographic process.
The competitiveness of a microphone circuit is mainly given by its performance (dynamic range, resolution, power consumption, clock jitter tolerance . . . ) and its cost (silicon area, MEMS sensor complexity, package size vs. sensitivity . . . ). In a typical MEMS microphone circuit, a MEMS microphone is coupled to an integrated circuit that biases the MEMS microphone, amplifies the output of the MEMS microphone, and performs and analog-to-digital conversion (ADC) on the electrical output of the MEMS microphone. Each of these functions consumes power and may consume valuable chip and/or board area. To reduce power consumption and chip area, conventional voltage-encoding-based sigma delta ADCs have been used as the ADC in microphone circuits. However, the sigma delta ADCs currently available have been pushed to technology limits and market trends require innovative solutions. Time-encoding-based solutions are promising alternatives to the voltage-encoding-based circuits conventionally used.